Healthcare Environmental Services has a transfer station for waste in Dundee and a storage, processing and incineration site at Shotts.

The BBC understands the Scottish sites are around the limits of the terms of their licence and that the company is co-operating fully with compliance officers from Sepa.

A UK government spokesman said it was monitoring the situation closely and had made sure that public services – including NHS Trusts – had contingency plans in place.

He added: “There is absolutely no risk to the health of patients or the wider public.

“Our priority is to prevent disruption to the NHS and other vital public services and work is under way to ensure organisations can continue to dispose of their waste safely and efficiently.”

‘Reduced incineration capacity’

The Scottish government said there had been no reports of any impact on these services from NHS boards in Scotland.

A spokesman added: “In the event of any disruption to service at NHS sites across Scotland, NHS Scotland already has contingency plans ready to put into place to ensure there is no impact on services to patients or staff.”

Healthcare Environmental Services said it had highlighted the reduction in the UK’s high-temperature incineration capacity for the last few years.

A spokesman added: “This is down to the ageing infrastructure, prolonged breakdowns and the reliance on zero waste to landfill policies, taking up the limited high-temperature incineration capacity in the market.

“Over the last year, this reduced incineration capacity has been evident across all of the industry and has affected all companies.”

At one site in Normanton, West Yorkshire, excess waste levels reached 350 tonnes in September, the HSJ reported.

She said: “If this is serious enough to have a criminal investigation, if it is also serious enough to go to a Cobra meeting – we know those meetings are reserved for the most serious incidents the government has to deal with – and yet there was no statement to Parliament, there was no statement to the public, no statement to the local community.

“I just don’t think that is fair.”

Unison’s head of health, Sara Gorton, described the situation as “simply horrific”, saying it was “unlikely that such a distressing situation would have happened had the service remained in-house”.